mpls ldp sesstion protection
what does that command is trying to solve?i cant understand what is the problem that command is trying to solve and when do we need to use this command?
im using this topology . here im using ospf for all these routers and prefix-suppresstion for all transit links. only loo are advertised for simplicity and mpls ip command is enabled on all phisical interfaces.
i thought that i need to use "mpls ldp sesstion protection " command if there is a physical link , for ex between R2 and R3 is failed/down, and i need to maintain all the mapping on R2 DB for 3.3.3.3 even if the physical link between R2 and R3 is down. but that not working like what i expected…
step1-
R2#show mpls forwarding-tableLocal Outgoing Prefix Bytes Label Outgoing Next HopLabel Label or Tunnel Id Switched interface2001 No Label 3.3.3.3/320 Fa1/0 10.1.23.3
as you can see here R3 is advertising 3 /32 directly to R2 because the outgoing label is “No label” which sounds weird to me because it should be “POP label” NOT " No Label" .
i tried do this on R2
R2(config)#mpls ldp session protection duration 30
this means “TO ME” that if the physical link between R2 and R3 is down, R2 is going to leveraging from the IGP and going to receive 3/32 from another route and is going to maintain this subnet into his LFIB even if the physical link between R2 and R3 goes down:
R2(config)#interface fastEthernet 1/0R2(config-if)#shutdown*Sep 13 05:58:59.079: %OSPF-5-ADJCHG: Process 1, Nbr 0.0.0.3 on FastEthernet1/0 from FULL to DOWN, Neighbor Down: Interface down or detached*Sep 13 05:58:59.099: %LDP-5-NBRCHG: LDP Neighbor 3.3.3.3:0 (1) is DOWN (Interface not operational)*Sep 13 05:59:01.027: %LINK-5-CHANGED: Interface FastEthernet1/0, changed state to administratively down*Sep 13 05:59:02.027: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0, changed state to downR2#show mpls forwarding-table 3.3.3.3Local Outgoing Prefix Bytes Label Outgoing Next HopLabel Label or Tunnel Id Switched interface2001 5001 3.3.3.3/320 Fa1/1 10.1.25.5
ok , R2 leveraging from IGP and get 3/32 from another path via fa1/1 and assign to him a local label 2001 as the same previous label, which is something also weird to me because why he did that? should he assigned a newer local label? and the outgoing label is 5001
step2-
lets try to do link failure between R3 and R6 but this time were not going to use "R2(config)[#mpls](javascript:void(0);) ldp session protection duration 30 " on R6 and lets see what will happened:
R6#show mpls forwarding-table 3.3.3.3Local Outgoing Prefix Bytes Label Outgoing Next HopLabel Label or Tunnel Id Switched interface18 No Label 3.3.3.3/320 Fa1/0 10.1.36.3R6(config)#interface fastEthernet 1/0R6(config-if)#shR6#*Sep 13 05:55:36.339: %OSPF-5-ADJCHG: Process 1, Nbr 0.0.0.3 on FastEthernet1/0 from FULL to DOWN, Neighbor Down: Interface down or detached *Sep 13 05:55:37.227: %SYS-5-CONFIG_I: Configured from console by consoleR6#*Sep 13 05:55:38.307: %LINK-5-CHANGED: Interface FastEthernet1/0, changed state to administratively down*Sep 13 05:55:39.307: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0, changed state to downR6#show mpls forwarding-table 3.3.3.3Local Outgoing Prefix Bytes Label Outgoing Next HopLabel Label or Tunnel Id Switched interface18 5001 3.3.3.3/320 Fa1/1 10.1.56.5
no difference between using “mpls sesstion protection” and not using “mpls sesstion protection”.
Q-1 why R2 assigned 3.3.3.3/32 with outgoing label “No Label” and not assigned it as " Pop Label"?
Q-2 why do we need to use “Mpls ldp session protection” if when i tried to use it affecting the exact same behavior when i don`t use it?
thanks